Slab heating device

ABSTRACT

Apparatus is provided for inductively heating a metal ingot or workpiece. The apparatus comprises a heating coil having convolutions spaced apart axially of the coil. The area within the coil is adapted to receive a workpiece to be heated, and means is provided to relatively reciprocate the coil and workpiece a distance equal approximately to one-half the pitch distance between adjacent convolutions of the coil, whereby more uniform heating of the workpiece surface is achieved. The convolutions of the coil are of rectangular configuration when viewed axially of the coil, and opposed portions of the convolutions are arcuately contoured in the direction of the coil axis, thus to increase the coil area available for heating the workpiece.

United States Patent [1 1 Vickers [54] SLAB HEATING DEVICE [75] inventor: Robert V. Vickers, Shaker Heights,

Ohio

[73] Assignee: Park-Ohio Industries, Inc., Cleveland, Ohio 22 Filed: July9, 1971 21 App1.No.: 161,277

[52] US. Cl. ..2l9/l0.57, 219/1067, 219/1073, 219/1079 [51] Int. Cl. ..H05b 9/02 [58] Field of Search..2l9/10.57, 10.73, 10.61, 10.67, 219/1079, 10.69, 10.71,10.75, 10.81

[4 1 Feb. 20, 1973 3,485,983 12/1969 Tama et al ..2l9/10.57

Primary Examiner-J. V. Truhe Assistant ExaminerB. A. Reynolds Attorney-James-l-l. Tilberry et a1.

[5 7] ABSTRACT Apparatus is provided for inductively heating a metal ingot or workpiece. The apparatus comprises a heating coil having convolutions spaced apart axially of the coil. The area within the coil is adapted to receive a workpiece to be heated, and means is provided to relatively reciprocate the coil and workpiece a distance equal approximately to one-half the pitch distance between adjacent convolutions of the coil, whereby more uniform heating of the workpiece surface is achieved. The convolutions of the coil are of rectangular configuration when viewed axially of the coil, and opposed portions of the convolutions are arcuately contoured in the direction of the coil axis, thus to increase the coil area available for heating the workpiece.

10 Claims, 7 Drawing Figures PATENTEDFEBEOW 3,717. 740

SHEET 1 BF 3 V INVENTOR n I R ROBERT v. VIICKERS A1 TORNEYS PATENTED BZO 75 3,717, 740

SHEET 2 OF 3 INVENTOR. ROBERT V. VICKERS BY Mew, 7114mm; 8 Bod ATTORNEYS SLAB HEATING DEVICE This invention relates to induction heating apparatus and, more particularly, workpiece support arrangement.

lnduction heating coils have been provided heretofore, comprised of convolutions of conductive tubing such a copper through which a liquid such as water is circulated for cooling the coil during ing operation. A workpiece to be inductively heated is disposed within the coil between the axially opposite ends thereof and the coil is connected to a suitable source of alternating current, whereby the workpiece is inductively heated when the coil is energized. When the coil is energized, the workpiece is heated both by induction and conduction, assuming, of course, that uniforn'i heating of the entire workpiece is desired as opposed to surface heating only. More particularly, the surface of the workpiece and a portion of the workpiece extendinginwardly from the surface is inductively'heated and heating of the remainder of the workpieceis achieved by the conduction of heat from the outer portions of the workpiece toward the center thereof; When surface heating alone is sought, high energyinduction heating is employed for a short period of time, whereby the surface of the workpiece is heated within such a short period' of time that conduction of heat inwardly of the workpiece is prevented.

in the use of induction heating apparatus heretofore known, uniform heating of the surface of a workpiece in the direction of the coil-axis is difficultto achieve and, in this respect, the areas of the workpiece between adjacent convolutions of the coil define gaps alongthe length. of the workpiece which are not inductively heated to the same extent as are the areas underlying the coil convolutions. This is disadvantageous, especially when rapid and uniform heating of the surface alone is desired.

A further disadvantage of induction heating coil structures heretofore known resides in the fact that the portions of the convolutions of the soil extending along or across a given surface of an ingot to be heated are linear when viewed in a direction extending toward that surface, whereby the area of the coil convolutions available for heatingthe underlying workpiece surface is limited. The area of a given heating coil disposed in proximity to the workpiece surface determines, in part, the amount of inductive heating which can be achieved by the coil. Accordingly, it is mostdesirable to provide the maximum coil area possible in order to increase coil heating ability.

The foregoing and other disadvantages of induction heating apparatus heretofore known are advantageously overcome in accordance with the present invention. in this respect, induction heating apparatus is provided wherein a coil-and workpiece are relatively reciprocable axially of the coil during heating of the workpiece to provide a more uniform heating of the surface of the workpiece. Accordingly, a more uniform heating of the interior portions of the workpiece by convection is achieved if total heating is desired. Further, in accordance with the present invention at least certain portions of the convolutions of the induction heating coil are provided with a non-linear configuration in order to increase the heating coil area and thusv the amount of heating achieved with a coil having a given axial length.-

to a heating coil and coil and an induction heat- In accordance with another aspect of the present in vention, a workpiece is supported for reciprocating movement relative to a heating coil and is reciprocated relative thereto a distance equal to approximately onehalf the pitch distance between adjacent convolutions of the coil. Such reciprocating movement providesfor surface areas of the workpiece between adjacent convolutions to be moved relative to the convolutions so that these areas, during the heating operation, are moved into and out of positions in which the most desirable inductive heating relationship exists therebetween. Thus, desirable uniform surface heating of the workpiece is achieved, whereby a desired surface temperature can be reached more rapidly than heretofore possible. Moreover, relative movement between the coil and workpiece provides for the use of a coil having a greater spacing between convolutions thereof than heretofore possible, whereby the coil can be produced using less material. It will be appreciated that this reduces the coil cost and, more importantly the coil resistance, whereby heating efficiency is increased.

In accordance with yet another aspect of the present invention, the heating coil is definedby opposed convolution portions lying in planes which are parallel to one another and to the axis of the coil. The portions of the convolutions in one of the pairs of planes are arcuately contoured in the direction of the coil axis, whereby the convolution portions are of a greater length than the linear distance between the opposite ends thereof. This configuration advantageously provides for increasing the coil area, as mentioned hereinabove.

Accordingly, an outstanding object of the present invention is the provision of induction heating apparatus which provides for increasing the efficiency of an induction heating operation.

Another object of the present invention is the provision of induction heating apparatus of the above character wherein the surface of a workpiece is more uniformly heated than heretofore possible.

Still another object of the present invention is the provision of induction heating apparatus of the above character wherein the surface of a workpiece is more uniformly heated than heretofore possible, thus to provide for more uniformly heating interior portions of the workpiece by conduction.

Still a further object of the present invention is the provision of induction heating apparatus of the foregoing character wherein relative reciprocation between a workpiece and coil is provided to achieve a more uniform induction heating of the surface of the workpiece.

Still another object of the present invention is the provision of induction heating apparatus of the foregoing character wherein the area of an induction heating coil of given length and cross-sectional dimension is increased, thus to increase the capacity of the coil to inductively heat a workpiece.

Yet another object of the present invention is the provision of induction heating apparatus of the above character wherein portions of the coil convolutions have a non-linear contour in the direction of the coil axis which provides for an increase in coil area and thus coil heating ability.

Still another object of the present invention is the provision of induction heating apparatus of the above character wherein the non-linear configuration of coil convolutions provides for increasing the coil area and wherein relative movement between the coil and an ingot to be heated provides for increasing the spacing between adjacent coil convolutions, whereby a more uniform and efficient induction heating of a workpiece is achieved.

The foregoing objects and advantages of the present invention will in part be obvious and in part more fully pointed out hereinafter in conjunction with the description of the drawing of a preferred embodiment of the invention and in which:

FIG. 1 is a perspective view of an induction heating coil arrangement in accordance with the present invention;

FIG. 2 is an elevational view, partially in section, illustrating a coil and ingot support mechanism made in accordance with the present invention;

FIG. 3 is a side elevation view of the apparatus of FIG. 2 and illustrating the ingot support in a position wherein the ingot is disposed in inductive heating relationship with the coil;

FIG. 4 is an end elevation view, looking from left to right, of the apparatus illustrated in FIG. 3;

FIG. 5 is a plan view, in section, of the ingot support mechanism, the view being taken along line 5-5 in FIG. 4;

FIG. 6 is a side elevation view, in section, of the ingot support mechanism, the section being taken along line 6-6 in FIG. 5; and

FIG. 7 is an end elevation view, in section, of the isngot support mechanism, taken along line 77 in FIG.

Referring now :to the drawing in greater detail wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting 'the same, FIG. 1 illustrates a preferred configuration of coil means made in accordance with the present invention. More particularly, coil means 10 is illustrated having opposite ends 12 and 14 connected to a suitable source of alternating current 16. Coil means 10 includes a plurality of convolutions 18, which are of rectangular configuration when viewed in the direction of coil axis A. Thus, convolutions 18 include portions 20 disposed in an opposed pair of planes substantially parallel to one another and to the coil axis A and portions 22similarly are disposed in a pair of opposed planes parallel to one another and to axis A. Further, portions 20 of the convolutions have a non-linear contour in the direction of axis A and, in the embodiment illustrated, are arcuate in contour. Thus, convolution portions 20 are longer than the linear distance between the opposite ends thereof, whereby an increase in convolution area is realized relative to the area which would be present if the convolution portions were of a linear configuration.

Although the shorter convolution portions 22 are illustrated as being of linear configuration, it will be appreciated that these portions also could be non-linear. Further, it will be appreciated, that the non-linear configuration could be other than the arcuate configuration illustrated in FIG. 1.

The area within coil means 10 is adapted to receive a metal ingot or workpiece W which, in the embodiment illustrated, is adapted to be positioned axially beneath coil means 10 and then elevated to a position within the coil so that the coil and workpiece are .in inductive heating relationship. Moreover, in accordance with the present invention, when ingot W is positioned within coil means 10 the coil means and ingot are adapted to be relatively reciprocated in the direction of coil axis A in order to more uniformly heat the ingot, as set forth more fully hereinafter.

Movement of ingot or workpiece W into inductive heating relationship with coil means 10, and relative reciprocating movement between the coil and workpiece can be achieved in any desired manner. A preferred arrangement for achieving positioning and relative reciprocating is illustrated in FIGS. 2-7 of the drawing. In this respect, coil means 10 is illustrated as being comprised of a continuous coil of tubing 24. Ends 12 and 14 of the coil means define inlet and outlet means, respectively, for a coolant such as water which is circulated through the coil tubing. The tubing is embedded in a body of refractory insulating material 26 and is open at its lower end for reception of workpiece W. The coil means may be closed at its upper end by a wall of insulating material if so desired.

Means is provided to support coil means 10 and ingot W in inductive heating relationship and, in the embodiment illustrated, the support means includes coil support means 28 and ingot support means 30. Support means 28 includes projection means 32 suitably attached to and projecting outwardly from coil means 10, and support means 34 may be defined, for example, by floor means, support rails, or the like. Support means 30 for workpiece W includes support surface means 36 such as a floor, wheeled ingot carrier means 38 and carrier elevating and lowering means 40. lngot carrier means 38 is movable in any suitable manner to position workpiece W in axial alignment with coil means 10. Preferably, support surface means 36 may be provided with rail means 42 and carrier elevating and lowering means 40 may be provided with rail means 44 which are horizontally alignable with rail means 42 to permit transfer of the wheeled carrier therebetween. Transfer of wheeled carrier means 38 may be accomplished in any suitable manner and, for example, the carrier may be provided with a slotted coupling component 46 adapted to loosely receive a T-heated rod component 48 which in turn is adapted to be reciprocated by suitable hydraulic or pneumatic motor means 50. Motor means 50 may be energized and controlled by any suitable means which are not illustrated. It will be appreciated that when the wheeled carrier means 38 is withdrawn from the position illustrated in FIG. 2 that an ingot or workpiece W may be removed from or positioned thereon, and that the wheeled carrier means may then be transferred along track means 42 and 44 to the position illustrated in FIG. 2. Stop means 45 are provided on track means 44 to limit movement of the carrier along the track means. Workpiece elevating and lowering means 40 may include any suitable hydraulic or pneumatic motor means 41 operable to elevate and lower wheeled carrier means 38 and thus workpiece W from the position illustrated in FIG. 2 to the position illustrated in FIGS. 3 and 4. Control and operation of motor means 41 does not form a part of the present invention and may be achieved in any desired manner. Track means 44 for wheeled carrier means 38 may be attached to suitable platform means 52 of the carrier elevating and lowering means, and guide means 54 may be provided to stabilize and guide movement of the platform and wheeled carrier means during elevation thereof. Coupling 46 and the T-head 49 on rod 48 are readily separable either manually or in response to elevation of carrier means 38 relative thereto to permit separation thereof when the carrier means is elevated and coupling thereof when the carrier is lowered.

As mentioned hereinabove, when coil means and ingot W are disposed in inductive heating relationship, means is provided to relatively reciprocate the coil means and ingot to achieve a more uniform heating of the ingot. Such relative reciprocation between the coil means and ingot may be achieved in any suitable manner. In accordance with the embodiment herein illustrated, such as relative reciprocation is achieved by reciprocating workpiece W vertically relative to coil means 10. More particularly, the reciprocating mechanism includes drive means 56 disposed laterally adjacent coil means 10 and carrier elevating and lowering means 40, and driven means associated with wheeled carrier means 38 and adapted to be operatively associated with drive means 56 when carrier means 38 is elevated to move ingot W into inductive heating relationship with coil means 10. Drive means 56, as is best illustrated in FIGS. 4, 5 and 7 of the drawing, includes a pair of gear elements 58 adapted to be driven by motor 60 which may, for example, be an electric motor. Motor 60 is suitably supported relative to support means 62 and is connected through gear box means 64 to shaft means 66 leading to one of the gears 58. The other of the gears 58 is attached to shaft means 68 which is driven in response to rotation of shaft means 66 by suitable sprocket and chain means 70 interconnecting shaft means'66 and 68. Gears 58 are of the same size and are driven at the same speed. As best illustrated in FIGS. 5, 6 and 7, wheeled carrier means 38 is comprised of a base portion 72 and a plate portion 74 which overlies base portion 72. Plate portion 74 is vertically reciprocable relative to base portion 72, and guide means such as angle irons 76 are suitably attached to the corners of base portion 72 to guide reciprocable movement of plate portion 74. Plate portion 74 can directly receive workpiece W, but preferably a support block 73 is disposed between plate 74 and workpiece W.

Base portion 72 supports a pair of rotatable axles 78 having wheel elements 80 which are positioned on the outer ends of the axles for rolling engagement with track means 42 and 44. Further, base portion 72 carries rotatable shaft means comprising a pair of shaft elements 82 which extend laterally from one side of the base portion and are provided on corresponding outer ends 83 thereof with a pair of gear elements 84. Shaft elements 82 further carry a plurality of eccentrics or cam elements 86 which are disposed in corresponding recesses 88 in the base portion and are rotatable with the corresponding shaft element. Cams 86 are rotated in response to rotation of shaft elements 82 and preferably are circumferentially oriented on the shaft elements in a manner whereby rotation thereof imparts uniform raising and lowering motion to plate portion 74 relative to base portion 72 in the manner set forth more fully hereinafter.

Plate portion 74, as best illustrated in FIGS. 6 and 7, is provided with a plurality of recesses 90 in the bottom surfaces thereof which are in overlying alignment with recesses 88 in base portion 72. An annular wheel element 92 is disposed in each of the recesses 90 and is supported for rotation therein by corresponding shaft means 94. The peripheral surfaces of each wheel 92 engages cam surface 96 of the corresponding cam element 86, and cam surfaces 96 are bounded on either side by flanges 98 which maintain the wheels and cams in proper lateral dispositions relative to one another. Gears 84 are of the same size, and are adapted to be moved vertically into cooperative meshing engagement with a corresponding one of thegears 58 when the wheeled carrier means is elevated to position workpiece W in inductive heating relationship with coil means 10. When so positioned, motor 60 is energized to rotate gears 58, whereby gears 84 are driven simultaneously and at the same rotational speed. Rotation of gears 84 imparts rotation to cam elements 86 which then rotate in engagement with wheels 92. Since cam elements 86 are eccentrically rotated relative to the axes shaft elements 82, plate means 73 is raised and lowered relative to base means 72 between the solid and broken line position of plate means 74 illustrated in FIG. 6. After inductive heating of workpiece W has been achieved, motor 60 is de-energized and elevating and lowering mechanism 40 is energized to lower the wheeled carrier from the position illustrated in FIGS. 3 and 4 to the position illustrated in FIG. 2. Hydraulic or pneumatic motor means 50 is then energized to withdraw wheeled carrier means 38 from beneath coil means 10 to facilitate removal of the heated ingot W therefrom and the placement of another ingot to be heated on the wheeled carrier means.

With reference once again to FIG. 1 of the drawing, it will be seen that the convolutions 18 of coil means 10 are spaced apart a distance P. The distance P is the distance between the adjacent sides of successive convolutions. The contour of cam elements 86 is such that plate means 74 is elevated and lowered a distance sufficient to provide for the area of ingot or workpiece W between the outer peripheries of adjacent convolutions to be reciprocated axially of the coil means a distance to assure that these surface areas together with the surface areas of the ingot therebetween are alternately brought into the most favorable disposition relative to the coil convolutions with regard to the inductive heating relationship between the coil means and the ingot.

The minimum distance required to assure the desired relative positioning between the coil means and workpiece will, of course, vary in accordance with the space between adjacent convolutions and the pitch or distance between the center line of adjacent convolutions. Reciprocation of the workpiece a distance equal to about one-half the pitch distance will most often provide the desired relative positioning between the workpiece and coil means. In any event, uniform heating of the outer surface and the underlying surface portions of the ingot is achieved by such movement and, ac-

' cordingly, a-more uniform heating of the inner portions of the ingot by conduction can be achieved if desired.

Further, by providing for relative reciprocating movement between the ingot and coil means, the spacing between adjacent coil convolutions can be increased without loss of heating efficiency. This advantageously provides for using less material in the construction of the coil without decreasing the heating ability of the coil. Moreover, the non-linear contour of portions of the convolutions assures a greater available area of coil for achieving the heating function.

While considerable emphasis has been placed herein on the fact that the ingot is reciprocated relative to the coil it will be appreciated that the coil means could be reciprocated relative to the ingot and that such coil reciprocation could be achieved by first positioning the coil relative to the ingot and then reciprocating the coil means relative to the ingot. Further, the ingot could be positioned relative to the coil in a manner similar to that herein described, and a coil could be reciprocated relative to the positioned ingot. Still further, relative reciprocation could be achieved by simultaneously reciprocating both the ingot and coil means. It will be appreciated too that elevating and lowering means 40 could be employed to reciprocate workpiece W relative to coil means 10 during the inductive heating operation. Moreover, it will be appreciated that the increased area of heating coil provided by the non-linear contour of portions of the coil convolutions can be employed to advantage without reciprocation between the coil means and ingot, and that relative reciprocation between the coil means and ingot can be used to advantage without providing for the coil means to have convolution portions of non-linear contour.

As many possible embodiments of the present invention may be made, and as many possible changes may be made in the embodiments herein set forth, it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the present invention and not as a limitation.

Having thus described my invention, Iclaim:

1. Apparatus for inductively heating a metal workpiece comprising, heating coil means having an axis and having convolutions spaced apart in the direction of said axis, means connecting said coil means to a source of alternating current, means for supporting said coil means and a workpiece to be heated in inductive heating relationship, said support means including workpiece support means having a base portion and a plate portion overlying said base portion and reciprocable relative thereto in the direction of said axis, driveable means between said base portion and plate portion for reciprocating said plate portion to reciprocate the workpiece relative to said coil means during induction heating of the workpiece, and means to drive said driveable means.

2. The apparatus of claim 1, wherein said workpiece is reciprocated relative to said coil means a distance approximately equal to $6 the pitch distance between adjacent coil convolutions.

3. The apparatus of claim 2, wherein said convolutions of said coil means lie in pairs of planes substantially parallel to one another and to said axis.

4. The apparatus of claim 3, wherein the portions of said convolutions lying in at least one of said pairs of planes have a non-linear contour in the direction of said axis.

5. The apparatus of claim 3, wherein the portions of said convolutions lying in at least one of said pairs of planes have an arcuate contour in the direction of said axis.

6. The apparatus of claim 5, wherein said portions of said convolutions are of greater length than the portions lying in the other of said pairs of planes.

7. The apparatus of claim 1, and means for reciprocating .said workpiece support means in the direction of said axis and between a first position in which a workpiece on said plate portion is axially outside said coil means and a second position in which the workpiece is disposed within said coil means.

8. The apparatus of claim 7, wherein said drivable means between said base portion and plate portion includes rotatable cam means and means for rotating said cam means, said drive means being fixedly supported relative to said workpiece support means and including means operatively engagable with said means for rotating said cam means when said workpiece support means is in said second position.

9. Apparatus for inductively heating a metal workpiece comprising heating coil means having an axis and having convolutions spaced apart in the direction of said axis, said convolutions lying in pairs of planes substantially parallel to one another and to said axis and the portions of said convolutions lying in at least one of said pairs of planes having an arcuate contour in the direction of said axis and being of greater length than the portions lying in the other of said pairs of planes, means connecting said coil means to a source of alternating current, means for supporting said coil means and a workpiece to be heated in inductive heating relationship and including coil support means and workpiece support means, said workpiece support means including support means movable to position a workpiece thereon within said coil means, means to reciprocate said movable support means axially relative to said coil means to reciprocate said workpiece a distance substantially equal to one-half the pitch distance between adjacent coil convolutions during induction heating of the workpiece, said movable support means including a base portion and a plate portion overlying said base portion and vertically reciprocable relative thereto, and said means to reciprocate said movable support means including rotatable cam means carried by said base portion and means to rotate said cam means, said cam means being operable upon rotation to reciprocate said plate portion.

10. Apparatus for inductively heating a metal workpiece having opposed pairs of parallel sides comprising, a heating coil adapted to surround a workpiece in inductive heating relationship with respect'thereto, said coil having an axis and having convolutions spaced apart in the direction of said axis, said convolutions lying in pairs of planes substantially parallel to one another and to corresponding opposed pairs of parallel sides of a workpiece disposed in said coil, the portions of said convolutions lying in at least one of said pairs of planes having an arcuate contour in the direction of said axis, means connecting said coil to a source of alternating current, means for supporting said coil and a workpiece to be heated in inductive heating relationship, and means to relatively reciprocate said coil and workpiece in the direction of said axis during induction heating of the work equal to one-half the coil convolutions. 

1. Apparatus for inductively heating a metal workpiece comprising, heating coil means having an axis and having convolutions spaced apart in the direction of said axis, means connecting said coil means to a source of alternating current, means for supporting said coil means and a workpiece to be heated in inductive heating relationship, said support means including workpiece support means having a Base portion and a plate portion overlying said base portion and reciprocable relative thereto in the direction of said axis, driveable means between said base portion and plate portion for reciprocating said plate portion to reciprocate the workpiece relative to said coil means during induction heating of the workpiece, and means to drive said driveable means.
 1. Apparatus for inductively heating a metal workpiece comprising, heating coil means having an axis and having convolutions spaced apart in the direction of said axis, means connecting said coil means to a source of alternating current, means for supporting said coil means and a workpiece to be heated in inductive heating relationship, said support means including workpiece support means having a Base portion and a plate portion overlying said base portion and reciprocable relative thereto in the direction of said axis, driveable means between said base portion and plate portion for reciprocating said plate portion to reciprocate the workpiece relative to said coil means during induction heating of the workpiece, and means to drive said driveable means.
 2. The apparatus of claim 1, wherein said workpiece is reciprocated relative to said coil means a distance approximately equal to 1/2 the pitch distance between adjacent coil convolutions.
 3. The apparatus of claim 2, wherein said convolutions of said coil means lie in pairs of planes substantially parallel to one another and to said axis.
 4. The apparatus of claim 3, wherein the portions of said convolutions lying in at least one of said pairs of planes have a non-linear contour in the direction of said axis.
 5. The apparatus of claim 3, wherein the portions of said convolutions lying in at least one of said pairs of planes have an arcuate contour in the direction of said axis.
 6. The apparatus of claim 5, wherein said portions of said convolutions are of greater length than the portions lying in the other of said pairs of planes.
 7. The apparatus of claim 1, and means for reciprocating said workpiece support means in the direction of said axis and between a first position in which a workpiece on said plate portion is axially outside said coil means and a second position in which the workpiece is disposed within said coil means.
 8. The apparatus of claim 7, wherein said drivable means between said base portion and plate portion includes rotatable cam means and means for rotating said cam means, said drive means being fixedly supported relative to said workpiece support means and including means operatively engagable with said means for rotating said cam means when said workpiece support means is in said second position.
 9. Apparatus for inductively heating a metal workpiece comprising heating coil means having an axis and having convolutions spaced apart in the direction of said axis, said convolutions lying in pairs of planes substantially parallel to one another and to said axis and the portions of said convolutions lying in at least one of said pairs of planes having an arcuate contour in the direction of said axis and being of greater length than the portions lying in the other of said pairs of planes, means connecting said coil means to a source of alternating current, means for supporting said coil means and a workpiece to be heated in inductive heating relationship and including coil support means and workpiece support means, said workpiece support means including support means movable to position a workpiece thereon within said coil means, means to reciprocate said movable support means axially relative to said coil means to reciprocate said workpiece a distance substantially equal to one-half the pitch distance between adjacent coil convolutions during induction heating of the workpiece, said movable support means including a base portion and a plate portion overlying said base portion and vertically reciprocable relative thereto, and said means to reciprocate said movable support means including rotatable cam means carried by said base portion and means to rotate said cam means, said cam means being operable upon rotation to reciprocate said plate portion. 